1. Field of the Invention
The invention relates to a process for the hydrophilizing and/or cement-residue-removing surface treatment of silicon slices or wafers by exposure to alkaline aqueous solutions containing hydrogen peroxide.
2. Description of the Prior Art
To produce electronic components from silicon, in most cases, silicon slices or wafers having at least one hydrophilic wafer surface are used. In this connection, the hydrophilic properties of the surfaces, which can be recognized qualitatively, for example, from the drainage behavior of a water drop applied to it, are usually produced as part of the treatment steps. These treatments are carried out subsequent to the polishing operation to remove adhering cement residues from the wafers and to finally clean the wafers before they are then packaged and passed on for despatch or storage.
A sequence of individual steps which basically goes back to a cleaning process (so-called "RCA cleaning") described by W. Kern and D. Puotinen in RCA Review, June 1970, pages 187 to 206 has gained wide acceptance for this treatment of polished wafers. In this case, adhering cement residues are removed with organic solvents, such as, for example, trichloroethylene, while the hydrophilizing step is carried out in a manner such that the silicon wafers are immersed in a bath containing an aqueous ammonia/hydrogen peroxide solution.
This procedure is, however, disadvantageous in a number of aspects. On the one hand, working with ammonia requires expensive exhaust plants just because of the nuisance caused by its smell. Furthermore, the bath has to be kept at elevated temperatures (usually 60.degree.-85.degree. C.) in order to achieve treatment times which are still economically acceptable. This results in an increased volatility of the ammonia so that, on the one hand, additional ammonia has to be supplied constantly and consequently the chemical requirements are correspondingly high. On the other hand, the ammonia concentration present in the bath is constantly subject to variations and this, in turn, has repercussions on the sensitive wafer surface. The phase in which the wafers are extracted from the bath and in the process are exposed to attack by the gaseous corrosive ammonia in the absence of the hydrogen peroxide which controls this reaction, has also proven to be particularly critical.
Another equally important disadvantage is the removal, usually before the hydrophilizing step, of the cement residues still adhering to the wafers after the polishing operation by means of organic, usually chlorine-containing solvents, such as trichloroethylene. In these solvents, it is particularly important to note the possible danger to health of the operating staff, the expensive preventative measures in terms of equipment necessitated thereby, such as exhausts and the like, and also the high costs of such solvents. In addition, in the case of all the solutions, it is difficult to remove interfering particles from the baths by filtration because of the high vapor pressure.